In general, surfaces of all substrates are easily stained after use, and cleaning of some of them is very difficult or requires the use of highly corrosive detergents. Using these detergents might be harmful for humans and the environment. Therefore, various antifouling or self-cleaning materials have been developed to maintain the cleanliness of substrates.
However, in today's processes for manufacturing antifouling coating materials, such as in a sol-gel reaction process, great amounts of organic solvents (such as alcohols, toluene, tetrahydrofuran, and so on) are required. Thus, the resulting coating materials contain a great amount of organic solvents (for example, over 90 wt %). These coating materials have a high volatile organic compound (VOC) value, for example, between 800 g/L and 900 g/L or even higher, therefore potentially resulting in environmental pollution.
Conventionally, in a sol-gel reaction for manufacturing a hydrophobic antifouling coating material, the reaction must be performed in an organic solvent due to the reactants being unstable in an aqueous solution, or having phase-separation or gelation problems. Although some waterborne resins, such as waterborne polyurethane (waterborne PU), have been used to proceed a sol-gel reaction in an aqueous solution, some organic solvents are still required in the process to stabilize the reaction. In addition, the resulting coating materials usually have poor hydrophobicity, and therefore are not appropriate for use as antifouling materials. Furthermore, waterborne polyurethane has poor weather-resistance and hardness, and is not suitable for outdoor use. Moreover, the molecular weight of the waterborne polyurethane is large and it has poor compatibility with existing systems, and as such its applications are limited.
Therefore, a novel antifouling coating material with a low VOC value is now required.